Applicant's invention relates to systems and methods for providing a verifiable chain of evidence and security for the transfer and retrieval of documents in digital formats.
Paper documents are the traditional evidence of the communications and agreements between parties in commercial and other transactions. Financial and real-estate transactions are protected by paper-based controls. Signatures and safety paper (such as pre-printed checks) facilitate detection of unauthorized alterations of the information of commercial transactions. Important documents may also be provided with "third man" controls, by the witnessing of signatures and by the seal and acknowledgement of a Notary Public.
The methods of commerce, however, have changed dramatically and continue to evolve. This is most evident in the replacement of paper-based communications with electronic communications. The "due care" controls used with paper-based communications do not exist in routine electronic transactions. Standard electronic communication does not provide the same ability to protect the authenticity and integrity of the communicated information.
When communication is by electronically reproduced messages such as e-mail, facsimile machine, imaging, electronic data interchange or electronic fund transfer, there no longer exists a signature or seal to authenticate the identity of the communicator. The traditional legally accepted methods of verifying the identity of a document's originator, such as physical presence or appearance, an ink signature, personal witness or Notary Public acknowledgement, are not possible.
The continued evolution of computer and telecommunications technology has regretfully been accompanied by the invention of more and more sophisticated ways to intercept and alter information electronically transmitted, including the widespread phenomenon of remote intrusion of computer systems through telecommunication links.
Some approaches to providing secure electronic commerce technology by data encryption give the user a verification mechanism for the integrity or privacy of the transmission that is controlled by the user and does not include the element of non-repudiation. At present, no distributed electronic document authentication system exists that can authenticate written or printed instruments in a manner that cannot be repudiated. No system provides electronic document verification based on a digital signature that cannot be repudiated, although some attempts have been described. See. e.g., D. Chaum, "Achieving Electronic Privacy", Scientific American, vol. 247, no. 8, pp. 96-101 (August 1992); C. R. Merrill, "Cryptography for Commerce--Beyond Clipper", The Data Law Report, vol. 2, no. 2, pp. 1, 4-11 (September 1994).
In contrast, Applicant's document authentication system (DAS) provides the needed security and protection of electronic transmissions. Most important to commercial and financial institutions, Applicant's DAS assumes the risk and responsibility of a document's authenticity. Applicant's DAS utilizes an asymmetric cryptosystem, known as a public-key system, to help ensure that the party originating an encrypted document is electronically identifiable as such.
Various aspects of public-key cryptographic (PKC) systems are described in the literature, including R. L. Rivest et al., "A Method for Obtaining Digital Signatures and Public-Key Cryptosystems," Communications of the ACM, vol. 21, pp. 120-126 (Febuary 1978): M. E. Hellman, "The Mathematics of Public-Key Cryptography", Scientific American, vol. 234, no. 8, pp. 146-152, 154-157 (August 1979); and W. Diffie, "The First Ten Years of Public-Key Cryptography", Proceedings of the IEEE, vol. 76, pp. 560-577 (May 1988). Popular PKC systems make use of the fact that finding large prime numbers is computationally easy but factoring the products of two large prime numbers is computationally difficult. A PKC system uses a key for decryption that is different from the key for encryption. Thus, a PKC user's encryption key can be public for use by others, and the difficulty of securely distributing keys may be avoided.
In general, information to be communicated just needs to be encrypted according to some system that the users have agreed in advance to use. Besides the PKC method, another encryption method is the data encryption standard (DES), which, as explained in W. Diffie et al., "Privacy and Authentication: An Introduction to Cryptography", Proc. IEEE vol. 67, pp. 397-427 (March 1979), is a classical cryptographic system. In general, a classical cryptographic system is a set of instructions, a piece of hardware, or a computer program that can convert plaintext (the unencrypted information) to ciphertext, or vice versa, in a variety of ways, one of which is selected by a specific key that is known to the users but is kept secret from others.
For either a classical or PKC system, the security of a message is dependent to a great extent on the length of the key, as described in C. E. Shannon, "Communication Theory of Secrecy Systems", Bell Sys. Tech. J. vol. 28, pp. 656-715 (October 1949).